Cosolvent electrolytes for electrochemical devices

ABSTRACT

A system and method for stabilizing electrodes against dissolution and/or hydrolysis including use of cosolvents in liquid electrolyte batteries for three purposes: the extension of the calendar and cycle life time of electrodes that are partially soluble in liquid electrolytes, the purpose of limiting the rate of electrolysis of water into hydrogen and oxygen as a side reaction during battery operation, and for the purpose of cost reduction.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/231,571 filed 31 Mar. 2014 which in turn claims benefit of U.S.patent application No. 61/810,684, the contents of these applicationsare hereby expressly incorporated by reference thereto in theirentireties for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under ARPA-E Award No.DE-AR000300 With Alveo Energy, Inc., awarded by DOE. The government hascertain rights in the invention.

FIELD OF THE INVENTION

The present invention relates generally to electrochemical devices, andmore specifically, but not exclusively, to cosolvent-based liquidelectrolytic cells.

BACKGROUND OF THE INVENTION

The subject matter discussed in the background section should not beassumed to be prior art merely as a result of its mention in thebackground section. Similarly, a problem mentioned in the backgroundsection or associated with the subject matter of the background sectionshould not be assumed to have been previously recognized in the priorart. The subject matter in the background section merely representsdifferent approaches, which in and of themselves may also be inventions.

A wide variety of battery technologies have been developed for portableand stationary applications, including lead acid, lithium-ion,nickel/metal hydride, sodium sulfur, and flow batteries, among others.(See Reference Number 1, below.) Not one of these technologies iscommonly used for applications related to the stabilization andreliability of the electric grid do to exorbitantly high cost, poorcycle and calendar lifetime, and low energy efficiency during rapidcycling. However, the development of lower cost, longer lived batteriesis likely needed for the grid to remain reliable in spite of theever-increasing deployment of extremely volatile solar and wind power.

Existing battery electrode materials cannot survive for enough deepdischarge cycles for the batteries containing them to be worth theirprice for most applications related to the electric grid. (See ReferenceNumber 1, below.) Similarly, the batteries found in electric and hybridelectric vehicles are long lived only in the case of careful partialdischarge cycling that results in heavy, large, expensive batterysystems. The performance of most existing battery electrode materialsduring fast cycling is limited by poor kinetics for ion transport or bycomplicated, multi-phase operational mechanisms.

The use of Prussian Blue analogues, which are a subset of a more generalclass of transition metal cyanide coordination compounds (TMCCCs) of thegeneral chemical formula A_(x)P_(y)[R(CN)₆]_(z).nH₂O (A=alkali cation, Pand R=transition metal cations, 0≦x≦2, 0≦y≦4, 0≦z≦1, 0≦n), has beenpreviously demonstrated as electrodes in aqueous electrolyte batteries.(See Reference Numbers 1-7.) TMCCC electrodes have longer deep dischargecycle life and higher rate capability than other intercalation mechanismelectrodes, and they enjoy their highest performance in aqueouselectrolytes. TMCCC cathodes rely on the electrochemical activity ofiron in Fe(CN)₆ complexes at high potentials. TMCCC anodes, on the otherhand, contain electrochemically active, carbon-coordinated manganese orchromium.

The development of a symmetric battery in which both the anode and thecathode are each a TMCCC is desirable because TMCCCs have longer cyclelife and can operate at higher charge/discharge rates than otherelectrode systems. If one TMCCC electrode were to be paired with adifferent kind of electrode, it is likely that the full battery wouldnot last as long, or provide the same high-rate abilities as a symmetriccell containing a TMCCC anode and a TMCCC cathode.

TMCCC cathodes are well understood, and the operation of a TMCCC cathodefor over 40,000 deep discharge cycles has been previously demonstrated.(See Reference Number 2.) These cathodes typically operate at about 0.9to 1.1 V vs. the standard hydrogen electrode (SHE). (See ReferenceNumber 8.) One challenge for the development of practical batteriesusing TMCCC cathodes is their trace solubility in aqueous electrolytes.Their partial dissolution into the battery electrolyte can result in adecrease in battery charge capacity due to mass loss from the electrodesand a decrease in efficiency due to side reactions with the cathode'sdissolution products.

The development of a TMCCC anode has proven much more challenging thanthat of TMCCC cathodes because these materials typically have reactionpotentials either near 0 V or below −0.5 V vs. SHE, but not in the rangebetween −0.5 V and 0 V that is most desirable in aqueous electrolytes,and because they operate only in a narrow pH range without rapidhydrolysis to manganese dioxide phases. (See Reference Numbers 8-9.) Asthe useful electrochemical stability window of aqueous electrolytes atapproximately neutral pH (pH=5-8) extends from about −0.4 V to 1 V vs.SHE, an anode reaction potential of 0 V results in a cell voltage lowerthan the maximum that is possible without decomposition of water. But,in the case of an anode reaction potential below −0.5 V vs. SHE, thecharge efficiency of the anode can be poor due to rapid hydrolysis ofwater to hydrogen gas. Finally, if the Mn(CN)₆ groups in the TMCCC anodehydrolyze, the capacity of the electrode is rapidly lost.

What is needed is a system and method for stabilizing TMCCC electrodesagainst dissolution and/or hydrolysis.

BRIEF SUMMARY OF THE INVENTION

Disclosed is a system and method for stabilizing electrodes againstdissolution and/or hydrolysis. The following summary of the invention isprovided to facilitate an understanding of some of technical featuresrelated to use of cosolvent electrolytes for more efficient and durablebatteries, and is not intended to be a full description of the presentinvention. A full appreciation of the various aspects of the inventioncan be gained by taking the entire specification, claims, drawings, andabstract as a whole. The present invention is applicable to otherelectrode types in addition to TMCCC cathodes and/or anodes, to otherelectrochemical devices in addition to full, partial, and/or hybridbattery systems including a liquid electrolyte.

This patent application concerns the use of cosolvents in liquidelectrolyte batteries for three purposes: the extension of the calendarand cycle life time of electrodes that are partially soluble in liquidelectrolytes, the purpose of limiting the rate of electrolysis of waterinto hydrogen and oxygen as a side reaction during battery operation,and for the purpose of cost reduction. Cosolvents are when two liquidsare combined into a single solution, as in the case of water and ethanolin wine, which may also contain dissolved compounds such as salts.Herein is demonstrated a utility of these cosolvent electrolytes usingthe model system of an aqueous sodium ion electrolyte battery containingTMCCC electrodes, but the benefits of cosolvents to the performance ofliquid electrolyte batteries apply generally to other electrode andbattery systems as well. One cost benefit occurs because an organiccosolvent as disclosed herein allows one to have a higher voltage beforewater is quickly split into hydrogen and oxygen. When the organiccosolvent is cheap, and the electrodes are the same materials (as insome embodiments disclosed herein when the anode has two differentreaction potentials), then the organic cosolvent lets theelectrochemical device have a higher voltage for about the samematerials cost. Energy is equal to the product of the charge and thevoltage, so a higher voltage electrochemical cell that gets more energyfrom the same materials will therefore have a lower cost/energy.

The present invention broadly includes a general concept of the use ofcosolvents in liquid electrolyte batteries, particularly, but notexclusively, in two areas: first, the concept of using cosolvents toprotect TMCCC electrodes from dissolution and/or hydrolysis, and second,the ability to use a hexacyanomanganate-based TMCCC anode with areaction potential so low that it can only be used when reduction ofwater to hydrogen gas is suppressed (as is the case, for example, when acosolvent is used as herein described).

Included herein is description of a novel method for the stabilizationof TMCCC electrodes against dissolution and hydrolysis, whilesimultaneously suppressing hydrogen generation at the anode: theaddition of a cosolvent to the aqueous electrolyte. A cosolventelectrolyte is one in which multiple liquid solvents are combined toform a single liquid phase, in which the electrolyte salt and anyadditional additives are then dissolved. The presence of a cosolvent candrastically change the solubility and stability of materials includingboth TMCCCs and electrolyte salts. The proper choice of cosolvent slowsor prevents the dissolution and/or hydrolysis of TMCCC electrodes, andit allows for the high-efficiency operation of TMCCC anodes withreaction potentials below −0.5 V vs. SHE. The final result is anelectrochemical device that operates at voltages of nearly double thosethat can be achieved in simple aqueous electrolytes, with longerelectrode cycle and calendar lives.

A battery (cell) that comprises an electrolyte and two electrodes (ananode and a cathode), one or both of which is a TMCCC material of thegeneral chemical formula A_(x)P_(y)[R(CN)_(6-j)L_(j)]_(z).nH₂O, where: Ais a monovalent cation such as Na⁺, K⁺, Li⁺, or NH₄ ⁺, or a divalentcation such as Mg²⁺ or Ca²⁺; P is a transition metal cation such asTi³⁺, Ti⁴⁺, V²⁺, V³⁺, Cr²⁺, Cr³⁺, Mn²⁺, Mn³⁺, Fe²⁺, Fe³⁺, Co²⁺, Co³⁺,Ni²⁺, Cu⁺, Cu²⁺, or Zn²⁺, or another metal cation such as Al³⁺, Sn²⁺,In³⁺, or Pb²⁺; R is a transition metal cation such as V²⁺, V³⁺, Cr²⁺,Cr³⁺, Mn⁺, Mn²⁺, Mn³⁺, Fe²⁺, Fe³⁺, Co²⁺, Co³⁺, Ru²⁺, Ru³⁺, Os²⁺, Os³⁺,Ir²⁺, Ir³⁺, Pt²⁺, or Pt³⁺; L is a ligand that may be substituted in theplace of a CN⁻ ligand, including CO (carbonyl), NO (nitrosyl), or Cl⁻;0≦x≦2; 0<y≦4; 0<z≦1; 0≦j≦6; and 0≦n≦5; and where the electrolytecontains water, one or more organic cosolvents, and one or more salts,where: the electrolyte is a single phase.

A rechargeable electrochemical cell, includes a positive electrode; anegative electrode; and an electrolyte having a total electrolyte volumeV including a first quantity of water comprising a first fraction V1 ofthe total electrolyte volume V and including a second quantity of one ormore organic cosolvents together comprising a second fraction V2 of thetotal electrolyte volume V; wherein V1/V>0.02; wherein V2>V1; wherein aparticular one electrode of the electrodes includes a transition metalcyanide coordination compound (TMCCC) material; and wherein theelectrolyte is a single phase.

A rechargeable electrochemical cell, includes a positive electrode; anegative electrode; and an electrolyte having a total electrolyte weightW including a first quantity of water comprising a first fraction W1 ofthe total electrolyte weight W and including a second quantity of one ormore organic cosolvents together comprising a second fraction W2 of thetotal electrolyte weight W; wherein W1/W>0.02; wherein W2>W1; wherein aparticular one electrode of the electrodes includes a transition metalcyanide coordination compound (TMCCC) material; and wherein theelectrolyte is a single phase.

A method for operating a rechargeable electrochemical cell having anegative electrode disposed in a single phase liquid electrolyte of atotal electrolyte quantity Q including at least a total quantity Q1 ofwater wherein Q1/Q is approximately 0.02 or greater and wherein anelectrolysis of the total quantity Q1 of water below a first potentialV1 initiates a production of hydrogen gas at a first rate R1, includinga) exchanging ions between the negative electrode and the liquidelectrolyte at an electrode potential VE, VE<V1; and b) producinghydrogen gas at a second rate R2 less than R1 responsive to theelectrode potential VE; wherein an electrolysis of the total electrolytequantity Q a second quantity of one or more organic cosolvents togethercomprising a second fraction Q2 of the total electrolyte quantity Qbelow a second potential V2 initiates the production of hydrogen gas atthe first rate R1, V2<V1; and wherein VE>V2.

Any of the embodiments described herein may be used alone or togetherwith one another in any combination. Inventions encompassed within thisspecification may also include embodiments that are only partiallymentioned or alluded to or are not mentioned or alluded to at all inthis brief summary or in the abstract. Although various embodiments ofthe invention may have been motivated by various deficiencies with theprior art, which may be discussed or alluded to in one or more places inthe specification, the embodiments of the invention do not necessarilyaddress any of these deficiencies. In other words, different embodimentsof the invention may address different deficiencies that may bediscussed in the specification. Some embodiments may only partiallyaddress some deficiencies or just one deficiency that may be discussedin the specification, and some embodiments may not address any of thesedeficiencies.

Other features, benefits, and advantages of the present invention willbe apparent upon a review of the present disclosure, including thespecification, drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, in which like reference numerals refer toidentical or functionally-similar elements throughout the separate viewsand which are incorporated in and form a part of the specification,further illustrate the present invention and, together with the detaileddescription of the invention, serve to explain the principles of thepresent invention.

FIG. 1 illustrates a schematic of batteries using the higher and loweranode reactions for CuHCF and MnHCMn;

FIG. 2 illustrates a unit cell of the TMCCC crystal structure;

FIG. 3 illustrates a cyclic voltammogram of MnHCMn in cosolvents;

FIG. 4 illustrates a cyclic voltammogram of MnHCMn in cosolvents;

FIG. 5 illustrates a cyclic voltammogram of MnHCMn in cosolvents;

FIG. 6 illustrates a cyclic voltammogram of MnHCMn in cosolvents;

FIG. 7 illustrates a cyclic voltammogram and integrated current ofMnHCMn in 90% MeCN;

FIG. 8 illustrates a cyclic voltammogram of CuHCF in cosolvents;

FIG. 9 illustrates a cyclic voltammogram of MnHCMn in 90% or 100% MeCN;

FIG. 10 illustrates a cycle life of MnHCMn in half cells;

FIG. 11 illustrates a set of potential profiles of MnHCMn in half cells;

FIG. 12 illustrates a cycle life of CuHCF in half cells;

FIG. 13 illustrates a set of GCPL vs. time profiles of MnHCMn vs. CuHCFin the full cell;

FIG. 14 illustrates a full cell voltage profile;

FIG. 15 illustrates a full cell voltage profile of the cell illustratedin FIG. 13; and

FIG. 16 illustrates a representative secondary electrochemical cellschematic having one or more TMCCC electrodes disposed in contact with acosolvent electrolyte as described herein

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention provide a system and method forstabilizing electrodes against dissolution and/or hydrolysis. Thefollowing description is presented to enable one of ordinary skill inthe art to make and use the invention and is provided in the context ofa patent application and its requirements.

Various modifications to the preferred embodiment and the genericprinciples and features described herein will be readily apparent tothose skilled in the art. Thus, the present invention is not intended tobe limited to the embodiment shown but is to be accorded the widestscope consistent with the principles and features described herein.

Definitions

The following definitions apply to some of the aspects described withrespect to some embodiments of the invention. These definitions maylikewise be expanded upon herein.

As used herein, the singular terms “a,” “an,” and “the” include pluralreferents unless the context clearly dictates otherwise. Thus, forexample, reference to an object can include multiple objects unless thecontext clearly dictates otherwise.

Also, as used in the description herein and throughout the claims thatfollow, the meaning of “in” includes “in” and “on” unless the contextclearly dictates otherwise.

As used herein, the term “set” refers to a collection of one or moreobjects. Thus, for example, a set of objects can include a single objector multiple objects. Objects of a set also can be referred to as membersof the set. Objects of a set can be the same or different. In someinstances, objects of a set can share one or more common properties.

As used herein, the term “adjacent” refers to being near or adjoining.Adjacent objects can be spaced apart from one another or can be inactual or direct contact with one another. In some instances, adjacentobjects can be coupled to one another or can be formed integrally withone another.

As used herein, the terms “couple,” “coupled,” and “coupling” refer toan operational connection or linking. Coupled objects can be directlyconnected to one another or can be indirectly connected to one another,such as via an intermediary set of objects.

As used herein, the terms “substantially” and “substantial” refer to aconsiderable degree or extent. When used in conjunction with an event orcircumstance, the terms can refer to instances in which the event orcircumstance occurs precisely as well as instances in which the event orcircumstance occurs to a close approximation, such as accounting fortypical tolerance levels or variability of the embodiments describedherein.

As used herein, the terms “optional” and “optionally” mean that thesubsequently described event or circumstance may or may not occur andthat the description includes instances where the event or circumstanceoccurs and instances in which it does not.

As used herein, the term “size” refers to a characteristic dimension ofan object. Thus, for example, a size of an object that is spherical canrefer to a diameter of the object. In the case of an object that isnon-spherical, a size of the non-spherical object can refer to adiameter of a corresponding spherical object, where the correspondingspherical object exhibits or has a particular set of derivable ormeasurable properties that are substantially the same as those of thenon-spherical object. Thus, for example, a size of a non-sphericalobject can refer to a diameter of a corresponding spherical object thatexhibits light scattering or other properties that are substantially thesame as those of the non-spherical object. Alternatively, or inconjunction, a size of a non-spherical object can refer to an average ofvarious orthogonal dimensions of the object. Thus, for example, a sizeof an object that is a spheroidal can refer to an average of a majoraxis and a minor axis of the object. When referring to a set of objectsas having a particular size, it is contemplated that the objects canhave a distribution of sizes around the particular size. Thus, as usedherein, a size of a set of objects can refer to a typical size of adistribution of sizes, such as an average size, a median size, or a peaksize.

As used herein, the term “electrolyte” means an ion-conducting, butelectronically insulating medium into which the electrodes of anelectrochemical cell are disposed. A liquid electrolyte contains one ormore liquid solvents and one or more salts that readily disassociatewhen dissolved in these solvents. Liquid electrolytes may also containadditives that enhance a performance characteristic of theelectrochemical cell into which the electrolyte is disposed.

As used herein, the term “battery” means a rechargeable electrochemicaldevice that converts stored chemical energy into electrical energy,including voltaic cells that may each include two half-cells joinedtogether by one or more conductive liquid electrolytes.

As used herein, in the context of a cosolvent solution and a majority orprimary solvent of such cosolvent solution, the term “majority” or“primary” means, for a two solvent cosolvent solution, a solvent having50% or greater volume of the total solvent volume (% vol./vol.), or 50%or greater weight of the total solvent weight (% weight/weight). For acosolvent solution having three or more solvents, the majority/primarysolvent is the solvent present in the greatest quantity (by volume orweight) as compared to the quantities of any of the other solvents ofthe cosolvent solution. These determinations are preferably made beforeaccounting for any salt or additive to the cosolvent solution. A“minority” or “secondary” solvent in a cosolvent solution is any othersolvent other than the majority/primary solvent. For purposes of thispresent invention when considering cosolvent solutions, water is never amajority solvent and may be a minority/secondary solvent. Water ispurposefully present as minority solvent in greater quantity than wouldbe incidental or present as a contaminant having 2% or greater volume ofthe total solvent volume (% vol./vol.), or 2% or greater weight of thetotal solvent weight (% weight/weight).

Electrode Materials

Some disclosed embodiments of the invention relate to battery electrodematerials in which dimensional changes in a host crystal structureduring charging and discharging are small, thereby affording long cyclelife and other desirable properties. Such dimensional changes canotherwise result in mechanical deformation and energy loss, as evidencedby hysteresis in battery charge/discharge curves.

Some embodiments relate to a class of transition metal cyanide complexcompound (TMCCC) electrode materials having stiff open frameworkstructures into which hydrated cations can be reversibly and rapidlyintercalated from aqueous (e.g., water-based) electrolytes or othertypes of electrolytes. In particular, TMCCC materials having thePrussian Blue-type crystal structure afford advantages including greaterdurability and faster kinetics when compared to other intercalation anddisplacement electrode materials. A general formula for the TMCCC classof materials is given by:

A_(x)P_(y)[R(CN)_(6-j)Lj]_(z).nH₂O, where:

-   A is a monovalent cation such as Na⁺, K⁺, Li⁺, or NH₄ ⁺, or a    divalent cation such as Mg²⁺ or Ca²⁺;-   P is a transition metal cation such as Ti³⁺, Ti⁴⁺, V²⁺, V³⁺, Cr²⁺,    Cr³⁺, Mn²⁺, Mn³⁺, Fe²⁺, Fe³⁺, Co²⁺, Co³⁺, Ni²⁺, Cu⁺, Cu²⁺, or Zn²⁺,    or another metal cation such as Al³⁺, Sn²⁺, In³⁺, or Pb²⁺;-   R is a transition metal cation such as V²⁺, V³⁺, Cr²⁺, Cr³⁺, Mn⁺,    Mn²⁺, Mn³⁺, Fe²⁺, Fe³⁺, Co²⁺, Co³⁺, Ru²⁺, Ru³⁺, Os²⁺, Os³⁺, Ir²⁺,    Ir³⁺, Pt²⁺, or Pt³⁺;-   L is a ligand that may be substituted in the place of a CN⁻ ligand,    including CO (carbonyl), NO (nitrosyl), or Cl⁻;-   0≦x≦2;-   0<y≦4;-   0<z≦1;-   0≦j≦6; and-   0≦n≦5.

Figures

FIG. 1 illustrates a schematic of batteries using the higher and loweranode reactions for the MnHCMn anode and the reaction potential of theCuHCF cathode. This schematic shows the operational modes of a batterycontaining a TMCCC cathode and a TMCCC anode used together in twodifferent electrolytes; 1) an aqueous electrolyte, and 2) a cosolventelectrolyte. In the aqueous electrolyte, rapid hydrogen evolution occursabove the lower operational potential of the anode, so only the upperoperational potential of the anode can be used. The result is a 0.9 Vcell. But, in the cosolvent electrolyte, hydrogen production issuppressed, resulting in efficient use of the lower operationalpotential of the anode and a full cell voltage of 1.7 V.

FIG. 2 illustrates a unit cell of the cubic Prussian Blue crystalstructure, one example of a TMCCC structure. Transition metal cationsare linked in a face-centered cubic framework by cyanide bridgingligands. The large, interstitiate A sites can contain water or insertedalkali ions.

FIG. 3 illustrates a cyclic voltammogram of MnHCMn in cosolvents. Cyclicvoltammetry of the lower operational potential of manganesehexacyanomanganate(II/I) is shown in aqueous 1 M NaClO₄ and 1 M NaClO₄containing various concentrations of acetonitrile. The position andhysteresis between the current peaks vary only slightly withacetonitrile concentration, indicating that the reaction mechanism andperformance is largely independent of the cosolvent.

FIG. 4 illustrates a cyclic voltammogram of MnHCMn in cosolvents. Cyclicvoltammetry of the lower operational potential of manganesehexacyanomanganate(II/I) is shown in aqueous 1 M NaClO₄ and 1 M NaClO₄containing 95% solvent volume acetonitrile and 5% solvent volume water.Reversible cycling is achieved even with only 5% water present. Thebackground current at −0.9 V is 1 mA in purely aqueous electrolyte, butonly 0.1 mA in the primarily organic cosolvent electrolytes,demonstrating improved coulombic efficiency with an organic primarycosolvent.

FIG. 5 illustrates a cyclic voltammogram of MnHCMn in cosolvents. Cyclicvoltammetry of the lower operational potential of manganesehexacyanomanganate(II/I) is shown 1 M NaClO₄ containing 5% solventvolume water, 47.5% solvent volume acetonitrile, and 47.5% solventvolume of one of sulfolane, propylene glycol monoethyl ether,hydroxypropionitrile, or gamma-valerolactone. In all cases, cycling ofMnHCMn is shown to be reversible.

FIG. 6 illustrates a cyclic voltammogram of MnHCMn in cosolvents. Cyclicvoltammetry of the lower operational potential of manganesehexacyanomanganate(II/I) is shown 1 M NaClO₄ containing 5% solventvolume water, 47.5% solvent volume acetonitrile, and 47.5% solventvolume of one of ethylene carbonate, dimethyl carbonate, or1,3-dioxolane, or containing 5% solvent volume water, 10% solvent volumeacetonitrile, and 85% solvent volume propylene carbonate. In all cases,cycling of MnHCMn is shown to be reversible.

FIG. 7 illustrates a cyclic voltammogram and integrated current ofMnHCMn in 1 M NaClO₄ in 90% solvent volume acetonitrile and 10% solventvolume water. Main Figure: cyclic voltammetry of MnHCMn(II/I) in 1 MNaClO₄, 90%/10% MeCN/H₂O shows an extremely reversible reaction centeredat −0.75 V vs. SHE. The open circuit potential of the material is abovethe upper reaction [MnHCMN(III/II)] so during the first reductive sweeptwo reactions are observed. The peak current of ±1.2 A/g is theequivalent of a 20 C galvanostatic cycling rate, indicating extremelyfast kinetics. Inset Figure: integration of the current during each scangives the specific charge and discharge capacity of the electrode. About57 mAh/g is observed, in close agreement with the approximatetheoretical specific capacity of 60 mAh/g. A coulombic efficiency ofwell over 95% is achieved. There is little capacity fading, in agreementwith GCPL measurements of MnHCMn(II/I) in the same electrolyte.

FIG. 8 illustrates a cyclic voltammogram of CuHCF in cosolventscontaining varying amounts of acetone. Cyclic voltammetry is shown ofthe copper hexacyanoferrate cathode in aqueous 1 M NaClO₄ and in 1 MNaClO₄ containing up to 90% solvent volume acetone and as little as 10%solvent volume water. There is little change in the potential of thereaction with increasing amounts of the cosolvent. No clear trend isobserved in the small effects of the cosolvent on the reaction potentialand kinetics of the charge and discharge of the electrode.

FIG. 9 illustrates a cyclic voltammogram of MnHCMn in 90% or 100% MeCN.Cyclic voltammetry is shown of the lower reaction manganesehexacyanomanganate(II/I) in 1 M NaClO₄ containing either 100% solventvolume acetonitrile or 90% solvent volume acetonitrile and 90% solventvolume water. The electrode has very poor kinetics and a poor currentresponse in the 100% solvent volume acetonitrile electrolyte. Incontrast, the addition of 10% water to the acetonitrile results in areaction with faster kinetics and a higher peak current.

FIG. 10 illustrates a cycle life of MnHCMn in half cells. During cyclingin 1 M NaClO₄ containing 90% solvent volume acetonitrile and 10% solventvolume water, MnHCMn(II/I) shows good cycle life, losing only 5% of itsinitial discharge capacity after 15 cycles. In contrast, in aqueous 1 MNaClO₄ with no acetonitrile present, 25% of the initial dischargecapacity is lost after 15 cycles.

FIG. 11 illustrates a set of potential profiles of MnHCMn in half cells.The potential profiles of MnHCMn(II/I) are shown during cycling in twodifferent electrolytes: aqueous 1 M NaClO₄ containing no organiccosolvent, and 1 M NaClO₄ containing 90% solvent volume acetonitrile and10% solvent volume water. In both electrolytes, the MnHCMn reaction iscentered at −0.95 V vs. Ag/AgCl, or equivalently, −0.75 V vs. SHE.Though both samples were cycled at the same 1 C rate, the sampleoperated in the purely aqueous electrolyte shows a much lower capacityof 40 mAh/g as rapid hydrolysis upon its insertion into the cellconsumed one third of its capacity. In contrast, the MnHCMn electrodeoperated in the electrolyte containing the organic primary cosolvent hada specific discharge capacity of over 55 mAh/g, much closer to themaximum theoretical value (see FIG. 10).

FIG. 12 illustrates a set of coulombic efficiencies of MnHCMn in halfcells operated by galvanostatic cycling between −0.95 V and −0.5 V vs.SHE. The coulombic efficiency is defined as the ratio for each cycle ofthe discharge capacity divided by the charge capacity. In the cellcontaining an electrolyte of 1 M NaClO₄ and 100% solvent volume water, acoulombic efficiency of less than 99% is observed. In three identicalcells each containing an electrolyte of 1.4 M NaClO₄, 95% solvent volumeacetonitrile, and 5% solvent volume water, a coulombic efficiency ofover 99.5% is observed.

FIG. 13 illustrates a cycle life of CuHCF in half cells. During cyclingof CuHCF at a 1 C rate in aqueous 1 M NaClO₄ containing no organiccosolvents, 4% of the initial discharge capacity is lost after 50cycles. In contrast, during cycling of CuHCF at a 1 C rate in 1 M NaClO₄containing 90% solvent volume acetonitrile and 10% solvent volume water,zero capacity loss is observed after 300 cycles.

FIG. 14 illustrates a set of GCPL vs. time profiles of MnHCMn vs. CuHCFin the full cell. The potential profiles of the CuHCF cathode andMnHCMn(II/I) anode in a full cell, and the full cell voltage profile areshown. The electrolyte was 1 M NaClO₄, 10% solvent volume H₂O, 90%solvent volume MeCN, and cycling was performed at a 1 C rate with theanode operated as the working electrode. An excess of CuHCF was used inthis case to avoid any oxygen generation at high potentials, so thepotential profile of the cathode is flatter than that of the anode.

FIG. 15 illustrates a full cell voltage profile. The full cell voltageprofile is of the cell shown in FIG. 13. The average voltage of the cellis 1.7 V, nearly double the voltage achievable if the MnHCMn(III/II)reaction is used. The result is a cell with significantly higher energyand power.

FIG. 16 illustrates a representative secondary electrochemical cell 1600schematic having one or more TMCCC electrodes disposed in contact with acosolvent electrolyte as described herein. Cell 1600 includes a negativeelectrode 1605, a positive electrode 1610 and an electrolyte 1615electrically communicated to the electrodes.

Overview

A battery (or cell) comprises an anode, a cathode, and an electrolytethat is in contact with both the anode and the cathode. Both the cathodeand the anode contain an electrochemically active material that mayundergo a change in valence state, accompanied by the acceptance orrelease of cations and electrons. For example, during discharge of abattery, electrons are extracted from the anode to an external circuit,while cations are removed from the anode into the electrolyte.Simultaneously, electrons from the external circuit enter the cathode,as do cations from the electrolyte. The difference in theelectrochemical potentials of the cathode and anode results in a fullcell voltage. This voltage difference allows energy to be extracted fromthe battery during discharge, or stored in the battery during charge.

The electrolyte in a battery allows ions to flow from one electrode tothe other, but that insulates the two electrodes from one anotherelectronically. Typically battery electrolytes include aqueous acids andsalts in lead acid and bases nickel/metal hydride batteries, and organicliquids containing lithium salts in lithium-ion batteries. Theelectrolyte may also contain additives that stabilize the electrodes,prevent side chemical reactions, or otherwise enhance batteryperformance and durability. The electrolyte may also contain multipleliquid components, in which case they are known as cosolvents. Theliquid component making up the majority of the electrolyte is typicallyknown as the primary solvent, while those making up the minority areknown as minority solvents.

Organic cosolvents have been used in battery electrolytes in some typesof batteries. For example, commercial lithium-ion battery electrolytescontain a variety of organic cosolvents, including ethylene carbonate,diethyl carbonate, propylene carbonate, and others. Those batteryelectrodes never include water as a minority solvent. Other aqueouselectrolyte batteries such as lead acid, nickel/metal hydride, and flowbatteries typically do not use cosolvent electrolytes. There is noprecedent among previously documented battery systems for cosolventelectrolytes containing water as a minority component.

An electrolyte containing organic cosolvents in combination with wateras a minority cosolvent offers several advantages in comparison toelectrolytes that are either primarily aqueous or that contain solelyorganic cosolvents. First, when water is present as only a minoritycosolvent, its decomposition into hydrogen and oxygen is suppressed, anda larger practical electrochemical stability window is achieved (FIGS.1, 4). Second, electrode materials and other battery materials that arewater-sensitive and may decompose by a hydrolysis mechanism are morestable when water is only a minority component of the system. Third,water has higher ionic conductivity than the organic solvents typicallyused in battery electrodes, so its presence as a minority cosolventincreases the electrolyte conductivity.

Cosolvent electrolytes are of interest for the stabilization of TMCCCelectrodes that have inherent solubility in aqueous batteryelectrolytes. Copper hexacyanoferrate (CuHCF) is a TMCCC recentlydemonstrated to be a high performance battery electrode. (See ReferenceNumber 2.) In the open framework structure of CuHCF, iron is six-fold,octahedrally coordinated to the carbon ends of the cyanide branchingligands, while copper is octahedrally nitrogen-coordinated (FIG. 3).Depending on the method of synthesis, the A sites in CuHCF may containpotassium or another alkali cation such as sodium or lithium, or anothertype of cation such as ammonium. More generally, for a TMCCC of thegeneral chemical formula A_(x)P_(y)[R(CN)₆]_(z).nH₂O, alkali cations A⁺and water occupy the interstitial A Sites, transition metal P cationsare six-fold nitrogen coordinated, and transition metal R cations aresix-fold carbon coordinated.

In the work described here, the electrochemical cells contained a TMCCCworking electrode, a counter electrode, an electrolyte in contact withboth the anode and cathode, and a Ag/AgCl reference electrode used toindependently measure the potentials of the anode and cathode duringcharge and discharge of the cell. When the electrode of interest was acathode material, then the working electrode was the cathode, and thecounter electrode was the anode. When the electrode of interest was ananode material, then the working electrode was the anode, and thecounter electrode was the cathode. In the case that the cell did notcontain both a TMCCC cathode and a TMCCC anode, a capacitive activatedcharcoal counter electrode was used to complete the circuit whileallowing the study of a single TMCCC electrode.

Electrochemical characterization of electrodes was performed usingcyclic voltammetry (CV) and galvanostatic cycling with potentiallimitation (GCPL). During the CV technique, the potential of the workingelectrode is swept at a constant rate between high and low cutoffpotentials, and the resulting current into or out of the electrode ismeasured. During the GCPL technique a constant current is applied to thecell until the working electrode reaches a maximum or minimum potential;upon reaching this potential extreme, the sign of the current isreversed.

Researchers have used TMCCCs as battery electrodes in cells containingaqueous and organic electrolytes (See Reference Numbers 12-24). Forexample, the reversible reduction of Prussian Blue to Everitt's Salt hasallowed its use as an anode in aqueous cells. (See Reference Numbers14-17 and 19-20.) However, the electrochemical potential of PrussianBlue is relatively high, so using it as an anode with a TMCCC cathoderesults in a low full cell voltage of 0.5-0.7 V vs. SHE. Such lowvoltages make these cells impractical, as many cells in series would berequired to achieve the high voltages needed for many applications.

Chromium hexacyanochromate (CrHCCr) has also been used as an anode infull cells that also contained Prussian Blue cathodes, and anaqueous/Nafion electrolyte. (See Reference Number 22.) The performanceof these cells was limited by the low potential and poor coulombicefficiency of CrHCCr in aqueous electrolytes and the use of acidicelectrolytes in which CrHCCr hydrolyzes.

TMCCC anodes containing electrochemically active hexacyanomanganategroups have also been recently demonstrated. Examples include manganesehexacyanomanganate (MnHCMn), and zinc hexacyanomanganate (ZnHCMn). Inhexacyanomanganate-based TMCCC anodes, the hexacyanomanganate groupsundergo two electrochemical reactions. First, Mn^(III)(CN)₆ can bereversibly reduced to Mn^(II)(CN)₆ at potentials near or above 0 V vs.SHE. Second, Mn^(II)(CN)₆ can be reduced to Mn^(I)(CN)₆ at lowerpotentials, typically below −0.4 V vs. SHE. In general, the lowerreaction cannot be efficiently used in aqueous electrolytes due to thesimultaneous generation of hydrogen gas at such low potentials. Oneexception is chromium hexacyanomanganate (CrHCMn), which has a lowerreaction potential of about −0.35 V, but high-purity CrHCMn isextraordinarily difficult to synthesize due to its affinity to formother phases such as mixed cyanides and oxides of chromium. In no priorart has the lower reaction of any hexacyanomanganate-based TMCCC beenused with high coulombic efficiency in aqueous electrolytes.

Though the use of a basic electrolyte would result in a lower potentialfor the onset of H₂ generation, TMCCCs rapidly decompose at high pHexcept in the presence of an excess of free cyanide anions, which are asevere safety hazard. Mildly acidic or neutral electrolytes are neededfor them to be stable. Thus, only the upper reaction of MnHCMn can beused without deleterious H₂ production. As the upper stability limit ofthese aqueous electrolytes is near 1 V, MnHCMn can be paired with acathode such as CuHCF to produce a battery with an average full cellvoltage of about 0.9-1 V.

TMCCCs have also been used as cathodes, but not as anodes, in organicelectrolyte batteries. (See Reference Numbers 12-13, 21, 23-24.) Mostcommonly, they have been used as cathodes in place of the standardLiCoO₂ cathode found in high-voltage organic electrolyte Li-ion cells. Anumber of studies have demonstrated TMCCCs containing electrochemicallyactive iron and/or manganese as cathodes in these high voltage cells.

TMCCCs have not been previously used as battery electrodes in cosolventelectrolytes in which water is a minority cosolvent. In recentlypublished patent application, we described the opportunity to do so forthe specialized case of water acting as the primary cosolvent. (SeeReference Number 7.) However, a practical cosolvent had not yet beenidentified, and the cosolvent electrolytes described in that documentdecompose into multiple phases under some circumstances, making themimpractical for use in an actual battery. In addition, in that previouswork, the idea of a cosolvent was described and claimed in the contextof an organic liquid additive to a water, with water as the primarysolvent of the electrolyte. Herein we describe for the first time theprinciples for selecting cosolvents and electrolyte salts to combinewith water to produce stable, single phase aqueous cosolventelectrolytes in which TMCCC electrodes operate with high efficiency,fast kinetics, and long lifetime. In addition, we demonstrate for thefirst time the operation of TMCCC electrodes in aqueous cosolventelectrolytes in which water is a minority solvent of the electrolyte,and an organic solvent is the primary solvent.

U.S. Patent Application No. 61/722,049 filed 2 Nov. 2012 includes adiscussion of various electrolyte additives to aqueous electrolytes, aswell as coatings on the electrodes of electrochemical cells, that canimprove a rate of capacity loss. U.S. Patent Application No. 61/760,402filed 4 Feb. 2013 includes a discussion of a practical TMCCC anode. Bothof these patent applications are hereby expressly incorporated in theirentireties by reference thereto for all purposes.

Herein we discuss and demonstrate for the first time the use of apractical aqueous cosolvent electrolyte for batteries containing a TMCCCanode and a TMCCC cathode. The use of an organic liquid as the primarysolvent, with water as a minority solvent has no significant effects onthe kinetics or reaction potentials of either TMCCC anodes or TMCCCcathodes as compared to the performance of those electrolytes in aqueouselectrolytes containing no organic solvents. In addition, the cosolventstabilizes TMCCCs against dissolution and hydrolysis, resulting ingreater electrode stability and longer cycle and calendar life.

Our previous demonstration of the operation of TMCCC cathodes incosolvent electrolytes did not demonstrate the use of an organic solventas the majority electrolyte, and it considered only the effect of anorganic minority cosolvent on the performance of TMCCC cathodes withoutshowing the reduction to practice of a full cell containing a cosolventelectrolyte. Furthermore, it did not address the extreme sensitivity ofhexacyanomanganate-based TMCCC anodes to electrolyte composition. Forthese reasons, among others, the work described here is novel andindependent.

The addition of an organic cosolvent as the majority component to thebattery electrolyte is especially important for the performance andlifetime of TMCCC anodes. Whereas without any cosolvents, the upperreaction of the MnHCMn anode must be used in aqueous electrolytes, herewe show that the addition of a cosolvent to the electrolyte suppresseselectrolysis of water to hydrogen gas. In a full cell also containing aCuHCF cathode, the result in an increase in average discharge voltagefrom about 0.9 V to about 1.7 V (FIG. 1). Nearly doubling the cellvoltage has extraordinary ramifications for the performance and cost ofthe battery. Energy scales proportionally with voltage, while powerscales with the square of the voltage. Thus, nearly doubling the voltagewhile using the same electrode materials results in about twice theenergy and nearly four times the power, at about the same materialscost. Without the presence of a cosolvent that limits the rate ofhydrogen production at the anode, cells with a TMCCC anode and cathodecannot achieve high efficiency at voltages above about 1.3 V. Thus, theaddition of the cosolvent increases the maximum practical voltage,energy, and power of the cell.

Prior study of Prussian Blue analogues in organic electrolytes didinclude the use of organic cosolvent electrolytes in some cases.However, in anhydrous conditions, the kinetics of TMCCC electrodes arevastly reduced, making these electrodes impractical for high powerapplications. In this work, we demonstrate for the first time the use ofaqueous cosolvent electrolytes containing non-negligible amounts ofwater. That water must be present for the TMCCC electrodes to be rapidlycharged or discharged.

As a first example, acetonitrile (also known as methyl cyanide, or MeCN)is chosen as a cosolvent to be used in electrolytes for batteriescontaining TMCCC electrodes. MeCN is fully miscible with water and iselectrochemically stable over a much wider potential range than wateritself. High purity, anhydrous MeCN is used in commercialultracapacitors. Here, reagent-grade MeCN was used, as low voltage cellsare less sensitive to electrolyte impurities that may result inparasitic side reactions at extreme potentials.

The choice of MeCN provides an additional benefit for the specific caseof a battery containing TMCCC electrodes. In a cosolvent electrolytecontaining MeCN as the primary solvent, the solvation shells of theTMCCC electrode particles will primarily be cyanide groups in whichnitrogen faces the particle. This completes the six-fold nitrogencoordination of P-site cations in the particle at the surface oradjacent to hexacyanometalate vacancies. The result is improved materialstability via suppression of dissolution via the formation of ahydration shell.

Other examples of organic solvents include ethylene carbonate, propylenecarbonate, and dimethyl carbonate; sulfolane; 1,3 dioxolane; propyleneglycol monoethyl ether; hydroxypropionitrile; diethylene glycol;gamma-valerolactone; acetone; ethylene glycol and glycerol. Organiccosolvents must be polar to allow them to form miscible single phasesolutions with water and a salt, but they may be either protic oraprotic.

It is desirable when using hexacyanomanganate-based TMCCC anodes to usewater as only a minority cosolvent, and organic liquids as the primarycosolvents. The manganese-carbon bond in hexacyanomanganate is labileand cyanide can be replaced by water and/or hydroxide. The choice of alarger, less polar organic species as the primary solvent results inweaker bonding to Mn and steric hindrance, both of which protect thehexacyanomananate group from suffering ligand exchange leading to itsdecomposition.

Proper selection of the electrolyte cosolvents, salts, and anyadditional additives will result in a single-phase system in which allof the components are miscible and do not phase segregate. Phasesegregation in a battery electrolyte is undesirable because iontransport will occur primarily in the phase containing the higher saltconcentration, while the other, less conductive phase or phases willimpede the transport of ions. It is not enough to simply choose liquidsthat are miscible, as the addition of a salt can lead to decompositionof the electrolyte into multiple phases: for example, one that is mostlywater, that has a high salt concentration, and that contains a smallamount of the organic solvent, and a second phase that is mostly organicsolvent, and contains little water or salt leads to poor performancewhen there is phase segregation, a problem addressed by proper selectionof electrolyte cosolvents.

A very limited number of common electrolyte salts that are highly watersoluble are also appreciably soluble in organic solvents. This isbecause most organic solvents have dielectric constants much lower thanthat of water. In other words, organic solvents are typically not aspolar as water, so the formation of a solvation shell during thedissolution of an ionic salt is not energetically favorable. Forexample, potassium nitrate, which has a saturation of 3.6 M in water atroom temperature, is only sparingly soluble in most organic solvents.

Here, to demonstrate the first reduction to practice of the operation ofTMCCC electrodes in cosolvent electrolytes containing an organic primarysolvent, we use sodium perchlorate hydrate as the electrolyte salt incosolvent electrolytes of water and MeCN. The choice of NaClO₄.H₂O isbased on its ability to dissolve in high concentrations (greater than 1M) over the entire range of cosolvent ratios from 100%/0% water/MeCN to0%/100% water/MeCN without forming biphasic systems.

The ternary phase diagrams describing the solubility of salts such asNaClO₄ in cosolvents such as water/MeCN are tabulated. The general needfor high salt concentration and a monophasic electrolyte can be used toselect other combinations of salts and cosolvents from these data.

Other cosolvents besides acetonitrile that can be used with water inelectrolytes for use in batteries containing TMCCC anodes include, butare not limited to, methanol, ethanol, isopropanol, ethylene glycol,propylene glycol, glycerine, tetrahydrofuran, dimethylformamide, andother small, polar linear and cyclic alcohols, polyols, ethers, andamines. However, while many of these solvents are fully miscible withpure water, they are not miscible in the presence of concentrated salt.For example, more than a few percent isopropyl alcohol willphase-segregate from concentrated aqueous salts of sodium, which thiswill not occur if acetonitrile is used in the place of isopropylalcohol. A proper selection of the cosolvents and the salt will resultin a single-phase solution.

CuHCF was synthesized as reported previously. An aqueous solution ofCu(NO₃)₂, and a second aqueous solution of K₃Fe(CN)₆ were added to waterby simultaneous, dropwise addition while stirring. The finalconcentrations of the precursors were 40 mM Cu(NO₃)₂ and 20 mMK₃Fe(CN)₆. A solid, brown precipitate formed immediately. It wasfiltered or centrifuged, washed, and dried. In a prior study, CuHCFsynthesized by this method was found to have the compositionK_(0.7)Cu[Fe(CN)₆]_(0.7).2.8H₂O. The CuHCF was found to have the cubicPrussian Blue open framework crystal structure using X-ray diffraction(XRD). The CuHCF was composed of nanoparticles about 50 nm in size, asverified by scanning electron microscope (SEM).

MnHCMn was produced state by adding a 10 mL aqueous solution containing0.0092 mmol KCN to a 10 mL aqueous solution containing 0.004 mmolMnCl₂.4H₂O under constant stirring in the dark in a nitrogen atmosphere.After stirring the solution for 20 minutes, the resulting dark greenprecipitate was centrifuged, washed with methanol, and dried at roomtemperature in a nitrogen atmosphere. Analysis of this material usingX-ray diffraction showed that it had the monoclinic crystal structurecharacteristic of MnHCMn(II) synthesized by a similar method (ReferenceNumber 24). Composition analysis using inductively coupled plasmaoptical emission spectrometry (ICP-OES) revealed that this material wasK_(0.4)Mn[Mn(CN)₆]_(0.6).nH2O (0<n<4).

Aqueous cosolvent electrolytes were prepared from reagent-gradeNaClO₄.H2O, de-ionized water, and reagent grade MeCN. All electrolyteswere pH-neutral, but not buffered. The salt was dissolved in aconcentration of 1 M in cosolvents with solvent volume ratios of100%/0%, 90%/10%, 50%/50%, 10%/90%, and 0%/100% water/MeCN.

Electrodes containing the freshly synthesized TMCCCs were prepared asreported previously. The electrochemically active material, carbonblack, and polyvinylidene difluoride (PVDF) binder were ground by handuntil homogeneous, and then stirred in 1-methyl-2-pyrrolidinone (NMP)solvent for several hours. This slurry was deposited on anelectronically conductive carbon cloth substrate using a doctor blade orspatula. Other substrates including foils and meshes of stainless steeland aluminum can also be used. These electrodes were dried in vacuum at60° C. For practical batteries, the binder is preferably selected suchthat it is stable against dissolution or excessive swelling in thecosolvent electrolyte, but is still fully wetted by the cosolvent.Methods for determining binder/electrolyte compatibilities such asHansen Solubility Parameter analysis are well known.

Activated charcoal counter electrodes were prepared by grinding thecharcoal with PVDF before stirring in NMP for several hours, followed bydeposition and drying on conductive substrates following the sameprocedure as in the case of electrodes containing a TMCCC.

Electrochemical Characterization

Half-cell measurements were performed on TMCCC electrodes in cosolventelectrolytes. The cell contained the working electrode, a Ag/AgClreference electrode, an activated charcoal counter electrode, and thedeaerated electrolyte. Cyclic voltammetry was performed on the workingelectrode.

EXAMPLE 1

A MnHCMn electrode was disposed in a half cell in the configurationdescribed above and operated by cyclic voltammetry. The reactionpotentials of the reactions of MnHCMn with 1 M Na⁺ were found to beabout −0.76 V and 0.04 V vs. SHE. The potential of the lower reaction ofMnHCMn varied only slightly with the addition of MeCN to theelectrolyte, from 0% MeCN to 95% MeCN (FIG. 3-4). The magnitude and signof the small shift in reaction potential showed no trend with MeCNconcentration (FIG. 3).). Furthermore, MnHCMn was found to cyclereversibly in 95% MeCN at with Na⁺ salt concentrations of both 1 M and1.4 M.

EXAMPLE 2

A MnHCMn electrode was disposed in a half cell in the configurationdescribed above and operated by cyclic voltammetry. MnHCMn was found tocycle reversibly in cosolvent electrolytes containing water as aminority cosolvent comprising 5% of the total solvent volume, and withequal quantities of MeCN and a second organic cosolvent comprising theremaining 95% of the total solvent volume (FIG. 5-6). These secondorganic cosolvents were one of: sulfolane, propylene glycol monoethylether, hydroxypropionitrile, gamma-valerolactone, ethylene carbonate,dimethyl carbonate, and 1,3-dioxolane. In these example electrolytes,the solvent volume of MeCN is as little as 10%, with another primaryorganic cosolvent such as propylene carbonate comprising 85% solventvolume. These electrolyte compositions of matter demonstrate the use ofmultiple organic cosolvents in combination with water as a minoritycosolvent.

EXAMPLE 3

A MnHCMn electrode was disposed in a half cell in the configurationdescribed above and operated by cyclic voltammetry. Over 55 mAh/g ofspecific discharge capacity was achieved for the lower reaction ofMnHCMn in a cosolvent electrolyte of 1 M NaClO₄ in 90% MeCN and 10%water (FIG. 7) This is comparable to the 50-60 mAh/g capacitiestypically achieved for the upper reaction of MnHCMn at 0.05 V in aqueouselectrolytes. With no loss in specific capacity of the anode, but a gainin full cell voltage of about 0.8 V, full cells that operate by usingthe lower reaction of MnHCMn will have nearly double the energy of thosethat operate by using the upper reaction of MnHCMn, with the sameelectrode materials (and associated costs). This makes the use of thelower reaction, and therefore, the use of a cosolvent electrolyte,critically important to the economics and viability of the battery.

EXAMPLE 4

A CuHCF electrode was disposed in a half cell in the configurationdescribed above and operated by cyclic voltammetry. The half cellscontained electrolytes of 1 M NaClO₄ and quantities of water and acetoneup to 90% acetone. During cyclic voltammetry the reaction potential ofCuHCF with 1 M Na⁺ was observed to be centered at 0.84 V vs. SHE, whichis consistent with the previously observed value (FIG. 8). The reactionpotential and peak current hysteresis of CuHCF during CV varied onlyslightly, 1 M NaClO₄ cosolvents containing increasing amounts of acetoneup to 90% of the total solvent volume.

EXAMPLE 5

A MnHCMn electrode was disposed in a half cell in the configurationdescribed above and operated by cyclic voltammetry. In this example, thehalf cell contained an electrolyte of pure MeCN and no water, and 1 MNaClO4. A much lower peak current of MnHCMn was observed in MeCNelectrolyte without water added as a minority cosolvent (FIG. 9). Incontrast, the CV curves shown in FIG. 3, FIG. 4, and FIG. 8 show thatthere is little change in the voltage difference between the peakcurrents in oxidation and reduction. This qualitatively indicates thatthe kinetics of the reaction of both MnHCMn and CuHCF with Na⁺ do notchange in the presence of MeCN, up to the case of a 95% MeCN primarysolvent. This example demonstrates that a minimum amount of water mustbe present in the cosolvent electrolyte to allow reversible electrodecycling that yields useful discharge capacity.

EXAMPLE 6

A MnHCMn electrode was disposed in a half cell in the configurationdescribed above and operated by cyclic voltammetry. In this example, thehalf cell contained an electrolyte of either pure water with no organiccosolvents and 1 M NaClO₄, or of 95% solvent volume basis MeCN, with 5%solvent volume basis water and 1 M or 1.4 M NaClO₄ (FIG. 4). Thebackground current observed at −0.9 V vs. S.H.E. was approximately 1 mAin the aqueous electrolyte containing no organic cosolvents. In the 95%volume basis MeCN electrolytes, the background current at −0.9 V vs.S.H.E. was less than 0.1 mA. Background current during a cyclicvoltammetry scan indicates a side reaction such as the decomposition ofwater that harms coulombic efficiency. This example demonstrates thatthe addition of a majority organic cosolvent results in an improvementin the coulombic efficiency of the MnHCMn anode.

EXAMPLE 7

A MnHCMn electrode was disposed in a half cell in the configurationdescribed above and operated by galvanostatic cycling at a 1 C ratebetween −0.9 V and −0.6 V vs. S.H.E. In aqueous 1 M NaClO₄ containing noorganic cosolvents, the MnHCMn electrode lost 25% of its initialspecific discharge capacity after 15 cycles (FIG. 10). However, in acosolvent electrolyte of 1 M NaClO₄ containing 90% solvent volume MeCNand 10% solvent volume water as a minority cosolvent, less than 5%capacity loss was observed after 15 cycles. This demonstrates that theuse of an organic cosolvent as the majority cosolvent solvent and wateras a minority cosolvent significantly increases the cycle lifetime ofthe MnHCMn anode.

EXAMPLE 8

A MnHCMn electrode was disposed in a half cell in the configurationdescribed above and operated by galvanostatic cycling at a 1 C ratebetween −0.9 V and −0.5 V vs. S.H.E. In aqueous 1 M NaClO₄ containing noorganic cosolvents, the MnHCMn electrode had an initial dischargecapacity of about 40 mAh/g. In 1 M NaClO4 containing 90% solvent volumeMeCN and 10% solvent volume water as a minority cosolvent, a specificdischarge capacity of about 55 mAh/g was achieved. This demonstratesthat the use of the organic primary cosolvent prevents the decompositionof MnHCMn that can result in significant, immediate capacity loss.

EXAMPLE 9

A MnHCMn electrode was disposed in a half cell in the configurationdescribed above and operated by galvanostatic cycling at a 1 C ratebetween −0.95 V and −0.5 V vs. S.H.E. In aqueous 1 M NaClO₄ containingno organic cosolvents, the MnHCMn electrode had coulombic efficiency ofless than 99% (FIG. 12). In 1.4 M NaClO₄ containing 95% solvent volumeMeCN and 5% solvent volume water as a minority cosolvent, a coulombicefficiency of over 99.5% was achieved in three identical cells.

EXAMPLE 10

A CuHCF electrode was disposed in a half cell in the configurationdescribed above and operated by galvanostatic cycling at a 1 C rate.CuHCF loses 4% of its initial capacity after 50 cycles at a 1 C rate inaqueous 1 M NaClO₄ (FIG. 13). In contrast, CuHCF is completely stableand shows zero capacity loss after 300 cycles when operated in anelectrolyte of 1 M NaClO₄ containing 90% solvent volume MeCN as theprimary cosolvent and 10% solvent volume water.

EXAMPLE 11

In this example, MnHCMn and CuHCF electrodes were disposed as anode andcathode, respectively, in a full cell also containing a referenceelectrode as described above. The electrolyte was 1 M NaClO₄ in 90%solvent volume MeCN and 10% solvent volume water. These full cells wereoperated such that the anode was controlled by the reference electrodeas the working electrode. The cathode was oversized such that thecapacity of the anode limited the capacity of the full cell. The MnHCMnanode was galvanostatically cycled at 1 C as the working electrodebetween −0.9 V and −0.5 V vs. SHE. Highly reversible cycling of the fullcell is achieved in this primarily organic cosolvent electrolyte (FIG.14). Negligible capacity loss of either the CuHCF cathode or the MnHCMnanode was observed for 30 cycles, as shown by the consistent duration ofeach cycle shown in FIG. 13. This full cell operates at an averagevoltage of 1.7 V, nearly double that of the 0.9 V cell achievable if theupper reaction of MnHCMn is used (FIG. 1, FIG. 7, and FIG. 15). As theelectrode materials in these two cells are identical, and only theirmode of operation is changed, the higher voltage cell offers nearlytwice the energy at the same materials cost. On a basis of the massesand densities of two TMCCC electrodes, a 1.7 V cell will have a specificenergy of 50 Wh/kg and an energy density of 90 Wh/L.

FIG. 16 illustrates a representative secondary electrochemical cell 1600schematic having one or more TMCCC electrodes disposed in contact with acosolvent electrolyte as described herein. Cell 1600 includes a negativeelectrode 1605, a positive electrode 1610 and an electrolyte 1615electrically communicated to the electrodes. One or both of negativeelectrode 1605 and positive electrode 1610 include TMCCC as anelectrochemically active material. A negative current collector 1620including an electrically conductive material conducts electrons betweennegative electrode 1605 and a first cell terminal (not shown). Apositive current collector 1625 including an electrically conductivematerial conducts electrons between positive electrode 1610 and a secondcell terminal (not shown). These current collectors permit cell 1600 toprovide electrical current to an external circuit or to receiveelectrical current/energy from an external circuit during recharging. Inan actual implementation, all components of cell 1600 are appropriatelyenclosed, such as within a protective housing with current collectorsexternally accessible. There are many different options for the formatand arrangement of the components across a wide range of actualimplementations, including aggregation of multiple cells into a batteryamong other uses and applications.

Electrolyte 1615, depending upon implementation, includes a set ofconditions that affect production of hydrogen and oxygen gas responsiveto the operating voltages of the electrodes. In general, at a firstelectrode voltage V1 relative to a reference electrode, initiation ofmore than an incidental quantity of hydrogen gas will begin to beproduced at a particular rate R1 that is consequential for theparticular application. Pure water, under comparable conditions, beginsthe production of hydrogen gas at rate R1 using a second electrodevoltage V2 that is greater than V1 (as shown in FIG. 1, this voltage isless negative). Cell 1600 may be operated at an electrode voltage lessthan V2 but greater than V1 to achieve a greater cell voltage betweenthe electrodes while producing hydrogen gas at second rate R2 less thanR1.

References: (The following references are expressly incorporated byreference thereto in their entireties for all purposes. These are thereferences that are cited throughout the preceding content.)

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The system and methods above has been described in general terms as anaid to understanding details of preferred embodiments of the presentinvention. In the description herein, numerous specific details areprovided, such as examples of components and/or methods, to provide athorough understanding of embodiments of the present invention. Somefeatures and benefits of the present invention are realized in suchmodes and are not required in every case. One skilled in the relevantart will recognize, however, that an embodiment of the invention can bepracticed without one or more of the specific details, or with otherapparatus, systems, assemblies, methods, components, materials, parts,and/or the like. In other instances, well-known structures, materials,or operations are not specifically shown or described in detail to avoidobscuring aspects of embodiments of the present invention.

Reference throughout this specification to “one embodiment”, “anembodiment”, or “a specific embodiment” means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment of the present invention and notnecessarily in all embodiments. Thus, respective appearances of thephrases “in one embodiment”, “in an embodiment”, or “in a specificembodiment” in various places throughout this specification are notnecessarily referring to the same embodiment. Furthermore, theparticular features, structures, or characteristics of any specificembodiment of the present invention may be combined in any suitablemanner with one or more other embodiments. It is to be understood thatother variations and modifications of the embodiments of the presentinvention described and illustrated herein are possible in light of theteachings herein and are to be considered as part of the spirit andscope of the present invention.

It will also be appreciated that one or more of the elements depicted inthe drawings/figures can also be implemented in a more separated orintegrated manner, or even removed or rendered as inoperable in certaincases, as is useful in accordance with a particular application.

Additionally, any signal arrows in the drawings/Figures should beconsidered only as exemplary, and not limiting, unless otherwisespecifically noted. Furthermore, the term “or” as used herein isgenerally intended to mean “and/or” unless otherwise indicated.Combinations of components or steps will also be considered as beingnoted, where terminology is foreseen as rendering the ability toseparate or combine is unclear.

The foregoing description of illustrated embodiments of the presentinvention, including what is described in the Abstract, is not intendedto be exhaustive or to limit the invention to the precise formsdisclosed herein. While specific embodiments of, and examples for, theinvention are described herein for illustrative purposes only, variousequivalent modifications are possible within the spirit and scope of thepresent invention, as those skilled in the relevant art will recognizeand appreciate. As indicated, these modifications may be made to thepresent invention in light of the foregoing description of illustratedembodiments of the present invention and are to be included within thespirit and scope of the present invention.

Thus, while the present invention has been described herein withreference to particular embodiments thereof, a latitude of modification,various changes and substitutions are intended in the foregoingdisclosures, and it will be appreciated that in some instances somefeatures of embodiments of the invention will be employed without acorresponding use of other features without departing from the scope andspirit of the invention as set forth. Therefore, many modifications maybe made to adapt a particular situation or material to the essentialscope and spirit of the present invention. It is intended that theinvention not be limited to the particular terms used in followingclaims and/or to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include any and all embodiments and equivalents falling within thescope of the appended claims. Thus, the scope of the invention is to bedetermined solely by the appended claims.

What is claimed as new and desired to be protected by Letters Patent of the United States is:
 1. An electrochemical system, comprising: a first electrode; a second electrode wherein at least one of said electrodes a transition metal cyanide coordination compound (TMCCC) material, said at least one electrode having a first dissolution rate R1 in a liquid electrolyte having an H₂0 component greater than 0.50; and electrolytic means, coupled to said electrodes, for decreasing said first dissolution rate R1, said electrolytic means including a total volume V having a first volume fraction V1 consisting essentially of H₂O, V1/V>0.02, V1/V<0.50, and a second volume fraction V2 of an organic cosolvent with V=V1+V2, V2>V1, and wherein said total volume V=V1+V2 consists essentially of a single phase.
 2. The electrochemical system of claim 1 wherein the TMCCC material includes a composition having the general chemical formula A_(x)P_(y)[R(CN)_(6-j)L_(j)]_(z).nH₂O, wherein: A includes one or more cations; P includes one or more metal cations; R includes one or more transition metal cations; and L is a ligand substituted in the place of a CN⁻ ligand; where 0≦x≦2; 0<y≦4; 0<z≦1; 0≦j≦6; and 0≦n≦5.
 3. The electrochemical system of claim 2 wherein: said A cations include one or more cations selected from the group consisting of Na⁺, K⁺, Li⁺, NH⁴⁺, Mg²⁺Ca²⁺ and combinations thereof; said P metal cations include one or more metal cations selected from the group consisting of Ti³⁺, Ti⁴⁺, V²⁺, V³⁺, Cr²⁺, Cr³⁺, Mn²⁺, Mn³⁺, Fe²⁺, Fe³⁺, Co²⁺, Co³⁺, Ni²⁺, Cu⁺, Cu²⁺, Zn²⁺, Al³⁺, Sn²⁺, In³⁺, or Pb²⁺ and combinations thereof; said R transition metal cations include one or more transition metal cations selected from the group consisting of V²⁺, V³⁺, Cr²⁺, Cr³⁺, Mn⁺, Mn²⁺, Mn³⁺, Fe²⁺, Fe³⁺, Co²⁺, Co³⁺, Ru²⁺, Ru³⁺, Os²⁺, Os³⁺, Ir²⁺, Ir₃₊, Pt²⁺, Pt³⁺, and combinations thereof; and said L ligands include one or more ligands selected from the group consisting of CO (carbonyl), NO (nitrosyl), Cl⁻, and combinations thereof.
 4. The electrochemical system of claim 1 wherein the total liquid volume V includes one or more cations selected from the group consisting of an alkali cation, an alkali earth cation, an ammonium cation, and combinations thereof.
 5. The electrochemical system of claim 4 wherein the liquid electrolyte produces a total concentration of said plurality of cations in the total liquid volume V greater than 0.1 M.
 6. The electrochemical system of claim 5 wherein said total concentration is greater than 1.4 M.
 7. The electrochemical system of claim 1 wherein the total liquid volume V includes an electrode lifetime extending additive; wherein an electrode disposed within the total liquid volume V includes a first lifetime when disposed in the total liquid volume V, wherein said electrode includes a second lifetime when disposed in the total liquid volume without said additive, and wherein said lifetime is greater than said second lifetime.
 8. The electrochemical system of claim 1 wherein the total liquid volume V includes one or more organic polar aprotic solvents.
 9. The electrochemical system of claim 8 wherein said one or more organic polar aprotic cosolvents include a particular cosolvent having one or more cyanide groups.
 10. The electrochemical system of claim 9 wherein said particular cosolvent includes acetonitrile.
 11. The electrochemical system of claim 8 wherein said one or more organic polar aprotic cosolvents include a particular cosolvent having one or more carbonate groups.
 12. The electrochemical system of claim 11 wherein said particular cosolvent is selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, and combinations thereof.
 13. The electrochemical system of claim 1 wherein the total liquid volume V includes one or more organic polar protic solvents.
 14. The electrochemical system of claim 13 wherein said one or more organic polar protic solvents include a particular solvent having one or more alcohol groups.
 15. The electrochemical system of claim 14 wherein said particular solvent is selected from the group consisting of methanol, ethylene glycol, glycerol, hydroxypropionitrile, and combinations thereof.
 16. The electrochemical system of claim 1 wherein V1/V≦30% and V2/V≧70%.
 17. The electrochemical system of claim 16 wherein V1/V≦10% and V2/V≧90%.
 18. The electrochemical system of claim 8 wherein the total liquid volume V includes both a cyanide-containing cosolvent and a carbonate-containing cosolvent.
 19. The electrochemical system of claim 8 wherein said one of more organic polar aprotic cosolvents include a particular cosolvent having one or more sulfone groups.
 20. The electrochemical cell of claim 19 wherein said particular cosolvent includes sulfolane.
 21. The electrochemical system of claim 8 wherein the total liquid volume V includes both a cyanide-containing cosolvent and a sulfone-containing cosolvent.
 22. The electrochemical system of claim 1 wherein said second volume fraction V2 includes a first volume subfraction V3 and a second volume subfraction volume V4 wherein V3+V4=V2, wherein said first volume subfraction V3 includes a first organic cosolvent, and wherein said second volume subfraction V4 includes a second organic cosolvent different from said first organic cosolvent.
 23. The electrochemical system of claim 22 wherein said first organic cosolvent includes MeCN, and wherein said second organic cosolvent includes a solvent selected from the group consisting essentially of sulfolane, propylene glycol monoethyl ether, hydroxypropionitrile, gamma-valerolactone, ethylene carbonate, dimethyl carbonate, propylene carbonate, and 1,3-dioxolan.
 24. The electrochemical system of claim 23 wherein V1/V=0.05, wherein V3/V≧0.10, and wherein V4/V≦0.85. 